For the internal fixation of the spinal column or portions thereof, preferably devices are used, which include pedicle screws, at least one longitudinal member, and connecting members for connecting the pedicle screws to the longitudinal member. The pedicle screws are screwed into the pedicle of the vertebra bodies, which are to be connected and fastened with their screw heads in the connecting member. In order to anchor the implant, the pedicle screws, on the one hand, must be anchored firmly in the pedicles of the vertebra bodies and, on the other, must be rigidly connect with the longitudinal member. The screw head and the connecting member may be connected by a clamping mechanism, which may be disconnectable, so that the implant may be removed without having to produce large openings in the tissue in the region of the spinal column.
A device for connecting a pedicle screw with a longitudinal member is disclosed in U.S. Pat. No. 5,728,098 to Sherman et al. This known device includes a pedicle screw with a spherical screw head and a connecting member having a cavity, which, towards the lower end adjoining the pedicle screw, is also constructed spherically to accommodate the screw head of the pedicle screw. At the upper end of the connecting member, a channel for accommodating a longitudinal member is disposed transversely to the longitudinal axis of the connecting member. Two sidewalls, forming the boundary of the channel, as well as the lower segment of the connecting member are elastically deformable transversely to the longitudinal axis. This enables, on the one hand, after the head of the pedicle screw is inserted, the lower segment of the connecting member to be compressed transversely to the longitudinal axis and, as a result, the screw head may be fixed in the cavity and, on the other hand, after the longitudinal member is placed in the channel, the upper segment of the connecting member may be compressed transversely to the longitudinal axis, so that the longitudinal member may be fixed in the channel between the sidewalls. The upper and lower ends of the connecting member are compressed by means of locking rings, which, for axial fixation, can be locked in position in grooves formed on the connecting member. It is a disadvantage of this device, however, that the locking ring, which fixes the longitudinal member in the upper segment of the connecting member, must be brought separately by the surgeon as an individual part to the implant after the longitudinal member is introduced into the channel, so that an additional step in the procedure is required. Moreover, bringing the locking ring over as a separate part increases the risk that the locking ring may be lost in the patient's body during implantation.